We have the same problem with dd and I have found that I have to strip my diapers almost every wash and also change her constantly. (I know you said you do but I mean like as soon as she pees) Even in my FB I use an extra fleece liner cause it helps to draw the moisture away a little more.

One other thing I have been doing is to coat her bum with some vaseline. Not thick and make sure to use a liner but that way she has a little barrier to keep the wet ness out. I hope that some of this helps you and your little one as I know the pain.

Oh, hugs mama- we are battling diaper rash right now too! I just don't know what to do either! Today I have spent the whole day stripping all of her dipes, so she's in sposies until that's finished, but her poor poor bottom!! And it hurts to wipe her and it hurts to put the vaseline or A&D ointment on, poor babe!!
I hope you get it all figured out! me too!

Could be the materials in the dipes? We can't use OV because my son's tushie has a reaction to it. We also had a little sensitivity to the fleece in FBs. Since switching to mostly all cotton fitteds and prefolds, no probs.